In a newly built liquid-cooled data center in Oregon, the operations manager once faced a vexing paradox: they had driven the PUE below 1.05 by adopting immersion cooling, yet they had to send someone every week to lift the heavy immersion tank lids and reseat the optical connectors soaked in coolant because of frequent optical module alarms. The root cause was that the housings of those standard commercial modules were never designed for immersion environments. Tiny seams gradually allowed liquid molecules to seep in under thermal expansion and contraction; additives in the coolant corroded some of the sealing materials; and the condensation caused by alternating hot and cold cycles intermittently degraded the optical path. The operations manager later remarked bluntly at an industry conference, "We turned our servers into submarines but forgot to put a wetsuit on the optical modules."
That story drove the creation of the HaloWill LiquidDefender series. Our engineering team started from scratch and re-examined every failure mode of optical modules in immersion environments. The first line of defense is the housing. LiquidDefender modules abandon the snap-fit or simple adhesive structures common in standard commercial modules, instead adopting a hermetically sealed cavity formed by continuous laser welding and dual fluororubber sealing rings. The cavity is filled with high-purity nitrogen, so that even when external coolant pressure fluctuates, no negative pressure is created inside to draw in moisture. All metal components that come into direct contact with the coolant are made from specialized corrosion-resistant alloys and are coated with a nano-scale liquid-repellent coating. In HaloWill's laboratory, a batch of our LiquidDefender modules has been continuously immersed in synthetic coolant for over five thousand hours. When opened for inspection, the interior remained as dry as the day it was sealed, with no signs of fogging or crystallization on any optical surface.
Physical sealing alone is not enough. The temperature characteristics of a liquid cooling environment are fundamentally different from traditional air cooling: at startup, the coolant temperature can be as low as 5°C or below, while under full load, the module shell temperature rises rapidly, and a significant temperature gradient exists between the laser inside the module and the external liquid. The bias current control algorithms of standard modules are prone to overshooting or lagging under such nonlinear temperature changes, causing optical power fluctuations. For this reason, LiquidDefender incorporates a multi-sensor fusion thermal management algorithm that simultaneously senses shell temperature, liquid temperature, and laser junction temperature, smoothly adjusting drive parameters in a feedforward manner. This compresses the optical power variation across the entire temperature range to within 0.5 dB. This wide-temperature real-time calibration capability has already been validated in the liquid-cooled training cluster of an autonomous driving company in North America, where the link bit error rate consistently remained better than ten to the power of negative fifteen after hundreds of cold starts and full-power cycles.
For scenarios employing two-phase immersion cooling—where the boiling and condensation cycles of the coolant bring more complex chemical and physical stress—HaloWill offers an optional enhanced condensation protection feature. A microporous breathable membrane and vapor capture structure are added at the optical interface end of the module, effectively preventing condensed droplets from invading the fiber end face. We have even deployed a humidity detection pixel inside the module; if a trace amount of packaging anomaly occurs, it can issue an early warning in the health data, allowing the operations team to replace the module calmly before a service disruption occurs.
In the North American market, we deeply understand that liquid cooling is not merely a technology choice, but also represents a commitment to sustainable development. The HaloWill LiquidDefender series ensures that this commitment does not have to compromise on optical interconnects. If you are operating or planning liquid-cooled infrastructure, we sincerely invite you to request validation samples and a full set of immersion test data customized for liquid-cooled environments. Let your optical modules coexist peacefully with your coolant, rather than always being the component that holds everything back.
